The present invention relates to a key switch device. More particularly, the present invention relates to a link-type key switch device suitably used for a slim keyboard of a notebook PC.
A related-art link-type key switch device is disclosed in Japanese Patent Publication No. 2001-283675A. As shown in FIG. 5, the related-art key switch device includes a board 1, a key top 2, a rubber spring 3 interposed between a board 1 and the key top 2, and a small link member 4 and a large link member 5 interposed between the board 1 and the key top 2. The rubber spring 3, the small link member 4, and the large link member 5 hold the key top 2 to allow the key top 2 to be movable up and down.
More specifically, the small link member 4 is made of a synthetic resin material. A lower end portion of the small link member is mounted on a slide guide (not shown) provided on the top surface of the board 1 so as to be slidable in a horizontal direction. A top shaft portion 7 is mounted on a bearing portion 8 provided on the rear surface of the key top 2 so as to be pivotable in a vertical direction. On the other hand, the large link member 5 is formed into a U-shape by bending a wire. An upper end portion of the large link member is mounted in a bearing portion 9 formed in the rear surface of the key top 2 so as to be pivotable in the vertical direction, and a lower end portion of the large link member is mounted in a bearing portion 10 formed on the top surface of the board 1 and the rear surface of the key top 2 so as to be pivotable in the vertical direction.
The key top 2 is held by a lifting mechanism including the small link member 4 and the large link member 5 and the rubber spring 3 so as to be movable up and down, thereby stably moving in a vertical stroke.
However, in a link mechanism of the related-art key switch device described above, the upper end portion of the large link member 5 is connected to the bearing portion 9 of a key top 2 so as to be pivotable in the vertical direction. And the lower end portion of the large link member 5 is connected to the bearing portion 10 of a board 1 so as to be pivotable in the vertical direction. With this structure, since the large link member 5 pivots about the bearing portion 10 of the board 1 in the vertical direction, the large link member 5 does not move directly downwards, but it moves in a horizontal direction by an interval D when the key top 2 is depressed. Accordingly, since at least the interval D must be secured as a gap between the key tops, a loss occurs when a plurality of key tops is arranged.
Furthermore, in the related-art key switch device, since only one small link member 4 is provided on one side of the key top 2, a wobbling in a sliding direction and a wobbling in a rotation direction of the key top 2 are easy to occur. Therefore, the wobbling deteriorates the touch of a key. In addition, in the related-art key switch device, the holding force of the key top decreases and the key top may be easily removed.